1. Field of the Invention
This invention relates to a radio communication apparatus and a radio communication method, which performs radio communication with a radio communication medium by using electromagnetic waves. In particular, the present invention relates to a radio communication apparatus and a radio communication method, in which sheets of paper such as negotiable securities and mail including a radio communication medium are continuously carried at high speed, and radio communication with the radio communication medium is established by making electromagnetic waves act on the radio communication medium incorporated in paper carried.
2. Description of the Related Art
FIG. 9 schematically illustrates an example of a conventional radio communication apparatus (for example, refer to Jpn. Pat. Appln. KOKAI Pub. No. 2000-105800). This radio communication apparatus has a carriage path 2 through which a radio communication medium 1 is carried in a direction of an arrow shown in FIG. 9. Actually, the radio communication medium 1 is carried in a state of being incorporated in paper (not shown) such as negotiable securities and mail. The term “a state of being incorporated” includes a state of included in paper and a state of being adhered onto a surface of the paper. In the middle of the carriage path 2, there is provided an antenna 4 of a radio main unit 3.
When the radio communication medium 1 carried through the carriage path 2 enters a communication area 5 of the radio main unit 3 (antenna 4), the radio communication medium 1 is supplied with operating electric power by an electromagnetic wave (carrier wave) radiated from the antenna 4. Then, when the supplied power reaches a predetermined level, the radio communication medium 1 changes to a state wherein it can receive a polling command from the radio main unit 3.
As shown in FIG. 10, the radio main unit 3 transmits a polling command at regular intervals through the antenna 4. Actually, the radio main unit 3 transmits a polling command by superposing a polling signal on a carrier wave. Specifically, the radio communication medium 1 which has entered the communication area 5 is supplied with power by a carrier wave, changes into a communicatable state, and performs radio communication with the radio main unit 3 in response to a polling command.
More specifically, the radio communication medium 1 which has entered the communication area 5 and been supplied with power receives a polling command transmitted from the radio main unit 3, and transmits a response to the radio main unit 3 while passing through the communication area 5. When the radio main unit 3 receives the response from the radio communication medium 1, the radio main unit 3 transmits reception data superposed on the received signal to a host apparatus (not shown). The reception data is data of value information if the radio communication medium 1 is incorporated in negotiable securities, and data of address information if it is incorporated in mail. Then, after the communication processing is completed, the radio main unit 3 starts transmission of a polling command again for a next radio communication medium 1 carried.
However, in the conventional radio communication apparatus described above, there are variations in timing at which the radio communication medium 1 carried through the carriage path 2 enters the communication area 5 of the antenna 4 of the radio main unit 3. Therefore, there are cases where the above sequence of communication, in which the radio communication medium 1 enters the communication area 5 of the radio main unit 3, receives a polling command transmitted from the radio main unit 3, and transmits a response, is not completed before the radio communication medium 1 passes through and goes out of the communication area 5.
For example, if the radio communication medium 1 is late in receiving a polling command, there are cases where the radio communication medium 1 cannot transmit a response while it is in the communication area 5 of the radio main unit 3. Such malfunction occurs more frequently as the carrying speed of the radio communication media 1 increases.
Further, for example, if the incorporating position of the radio communication medium 1 in negotiable securities is shifted from the center thereof, positions of the radio communication media 1 when passing through the antenna 4 vary according to the carrying state of the negotiable securities (orientations of the securities, such as whether the front side is up or the back side is up, and whether each security is placed upside down or not). Therefore, if the antenna 4 set in a fixed position with respect to the carriage path 2 is used for radio communication, it cannot provide stable communications to all radio communication media 1 having different carrying states, and communications are sometimes impossible.